This invention relates to a process and apparatus for recovering chlorine by causing oxygen or a gas containing oxygen to act on iron chloride or a gas containing iron chloride as the predominant constituent.
More specifically, the invention relates to a process for recovering chlorine from iron chloride, which comprises introducing into an oxidation furnace iron chloride or a gas containing iron chloride as the predominant constituent (hereinafter referred to inclusively as "iron chloride gas") and causing oxygen or a gas containing molecular oxygen (hereinafter referred to inclusively as an "oxidizing gas") to react with the iron chloride gas thereby to prevent adhesion of the iron oxide thus produced to the furnace walls and, at the same time, to recover chlorine with high efficiency, whereby stable operation of the oxidation furnace over a long period is made possible.
The basic concept of causing iron chloride and oxygen to react thereby to recover chlorine is known, and various processes for reducing this concept to practice have been proposed as in the following references.
1. U.S. Pat. No. 3,376,112.
The specification discloses a method wherein FeCl.sub.3 is rendered into the double salt NaFeCl.sub.4 with NaCl, and for causing this double salt to react with oxygen, a moving-bed type oxidation furnace packed with small spheres of inactive material of a diameter of approximately 3 mm. is used, the movements of these small spheres functioning to prevent the Fe.sub.2 O.sub.3 of the reaction products from adhering to the interior surfaces of the furnace. By this method, however, since the furnace is filled with the small spheres, the processing capacity per unit interior volume of the furnace is small, and if a large furnace is used, the movements of the small spheres therewithin can become a less uniform flow, and adhesion of Fe.sub.2 O.sub.3 at parts where this flow can become stagnant cannot be avoided.
2. U.S. Pat. No. 2,642,339.
A fluidized bed oxidation furnace in which Fe.sub.2 O.sub.3 powder is utilized as a catalyst for oxidation reaction of iron chloride is proposed. Fe.sub.2 O.sub.3 of the reaction products which adheres to and tends to grow on the furnace walls is scraped off by the flow of the Fe.sub.2 O.sub.3 powder arising from the blowing in of the reaction gases. However, a method of solving the problem of solidification of the fluidized bed due to sintering of the iron oxide formed which can occur locally at the part where the reaction gases are blown in is not indicated with respect to the case of a practical furnace of large scale. Furthermore, in the case where the origin of formation of the iron chloride is a chloridization furnace of fluidized bed type, the process involves a two-stage fluidized reaction in which the above-mentioned oxidation furnace is added, and complication control procedures may be required in the operation.
3. U.S. Pat. No. 3,325,252.
An oxidation furnace of flame type is proposed. In the use of this furnace, iron chloride and oxygen are injected through respective coaxial nozzles and thus caused to react. It has been found through my experience, however, that the Fe.sub.2 O.sub.3 adheres rapidly in great quantity to the tips of the injection nozzles and the furnace wall in the vicinity of the injection nozzles in this type of furnace, whereby the furnace can become clogged in a short time.
4. U.S. Pat. No. 3,092,456.
Through the use of an oxidation furnace of the same type as in the above reference (3), CO or fine powder coke is blown in onto the furnace walls or discharge pipe parts where adhesion of Fe.sub.2 O.sub.3 occurs with the aim of preventing this adhesive deposition of Fe.sub.2 O.sub.3 by causing the free oxygen remaining after the reaction to combine with the CO or fine powder coke.
5. French Pat. No. 1,315,838.
It is disclosed that adhesion of Fe.sub.2 O.sub.3 can be prevented by maintaining the temperature of the oxidation furnace from 10.degree. to 50.degree. C higher than the reaction gas temperature.
However, so far as I know, none of the oxidation furnaces of the above cited proposed methods has been successfully reduced to industrial practice. The principal reason for this may be that the adhesive depositing of the Fe.sub.2 O.sub.3 of the reaction products on the furnace walls cannot be completely prevented and inevitably gives rise to clogging of the furnace, whereby the operation of the furnace must be frequently stopped for removing the adhesive deposit. Furthermore, in the case where a large furnace is used in the process of each of the above cited patents, the practice of the invention is accompanied by technically great difficulties, whereby such a measure is not necessarily practical. Further, while it is required to strictly control the reaction temperature distribution and residence time at each reaction temperature, and some of the above cited processes refer to the division of a reaction furnace into two zones, such conventional processes are not considered sufficient in controlling the reaction temperature distribution in relation to the residence time at each temperature.